Fiber optic loop signal coupler apparatus

ABSTRACT

Fiber optic rotary coupler apparatus is disclosed in which a light signal formed in a continuous ring in a plane is transmitted between a barrel and a surrounding sleeve within which the barrel is rotatably mounted. The light signal ring is produced by a light source and an associated light transmitting fiber wound on the barrel in at least one complete circular loop of a radius such that a portion of a light signal introduced into an end thereof is transversely radiated from the fiber. Light detector means, which may include a further optical fiber for transmitting light signals to a remote detector, is carried on the sleeve. In one embodiment, a plurality of optical and electrical signal channels are incorporated into a single device.

BACKGROUND OF THE INVENTION

The present invention relates generally to apparatus for transmittingsignals between two relatively rotatable members. More specifically, theinvention involves signal coupler apparatus wherein light signals in acontinuous ring in a plane are transmitted between rotatable memberswithout physical contact. The invention offers particular advantages inlow cost, multiple channel rotary signal coupler apparatus.

Requirements to transmit electrical power and data across rotary jointshave existed for many years. Traditionally, such functions wereaccomplished with electromechanical sliding contact slip rings. Earlyslip ring applications, including those for data transmission, typicallyinvolved the transmission of appreciable amounts of power. Slidingcontacts were well suited to transmission of signals characterized bysignificant voltages and/or currents.

As technologies requiring the use of slip ring apparatus progressed, theinherent characteristics of electromechanical slip rings began to imposeincreasingly severe limitations on system performance. Morespecifically, advancing technologies required increased channel capacitycombined with overall size reduction, decreased cross coupling ofsignals on separate channels, and decreased noise, dead band and powerconsumption. Attempts to reduce friction levels by reducing contactpressure increased the susceptibility of sliding contacts to lift duringvibration, thereby introducing noise and/or signal interruptions. Inaddition, the lower power levels of contemporary data signals tended toreduce immunity to contact contamination, and consequently to increasethe likeihood of signal interruption and/or distortion.

An additional limitation on the use of electromechanical slip ringsrelates to cost. Precious metals have been used to provide goodelectrical conduction at low contact forces, and to decrease the amountof maintenance required to keep contact surfaces adequately free ofcontamination and oxides. Modern plating techniques have helped toreduce the cost of precious metals required in a slip ring assembly.Nevertheless, the precious metal cost for a typical small assembly isseveral hundred dollars. An additional cost item arises from cleaningand maintenance operations which are routinely necessary several times ayear, and which require the services of specially trained andexperienced technicians.

one technology which has recently shown considerable promise forovercoming the noted problems involves the transmission of light signalsbetween relatively rotating members. In general, the known devicesutilizing this techique comprise a pair of members, one of which isrotatable with respect to the other about an axis of rotation. One ofthe members carries a light detector which is aligned with a lightsource carried by the other member. Accordingly, light signals, whichmay be modulated to convey data or information of interest, aretransmitted across the moving/stationary interface without physicalcontact between the relatively moving members. Typical known forms ofsuch devices are disclosed in U.S. Pat. Nos. 3,401,232, 3,922,063 and4,027,945 issued respectively to J. S. Goldhammer et al on Sept. 10,1968, F. A. Marrone on Nov. 25, 1975 and M. L. Iverson on June 7, 1977.Each disclosed device employs a light source and a detector alinged withthe axis of rotation. Multiple channels may be provided by arranginglight sources and detectors on the axis of rotation and in concentricrings about the axis.

Such arrangements are practical and satisfactory for small numbers ofchannels. However, for larger numbers of channels the required areaperpendicular to the axis of rotation becomes prohibitively large sincethe area increases approximately as the square of the number ofchannels. Further, where the light source and/or detector areimplemented by spreading out the ends of light transmitting fibers of afiber bundle into a ring as disclosed in U.S. Pat. No. 4,027,945, thenumber of fibers required to implement individual channels variesapproximately as the square of the radius of the rings. For largerrings, a very large number of fibers becomes necessary, and it becomesincreasingly difficult to evenly distribute the light signal around thering. Further, such construction is generally somewhat unconventional,and the complexities of suitably distributing and maintaining alignmentof the fibers contributes to the cost of the device.

The applicant has devised an optical rotary coupler design in which asingle optical fiber or small fiber bundle formed in a circular loop isemployed to radiate light signals transversely to an axis of rotation.The design is exceptionally simple and capable of implementation with alarge number of identical channels axially spaced along the axis ofrotation. Further, the design minimizes the necessity for complexdistribution and alignment of fibers in an optical fiber bundle.Accordingly, the advantages of using light signals to transmit dataacross a rotating/stationary interface are provided at minimum cost.

SUMMARY OF THE INVENTION

The applicant's unique fiber optic rotary coupler apparatus basicallycomprises a light transmitting fiber through which light is normallylongitudinally transmitted, and from which light escapes or is acceptedtransverse to the length of the fiber if it is bent into a radius withina predetermined range of radii. The fiber is carried on a first memberwhich is rotatable relative to a second member about an axis ofrotation, and which maintains the fiber in at least one completecircular loop having a radius within the predetermined range, the loopbeing centered on the axis of rotation and generally lying in a planeperpendicular thereto. A light source or detector fixed relative to thefirst member is oriented to project light signals into an end of thefiber, or to receive light signals therefrom. A light detector or sourcecarried by the second member is positioned to receive light signalstransversely radiating from the fiber, or to project light signalstransversely into the fiber. The fiber may be arranged so that both endsthereof are positioned to receive light signals from the light source. Amultiple channel device may be implemented by arranging a plurality ofidentical fiber loops and corresponding light detectors along the axisof rotation.

The primary object of this invention is to provide an exceptionallysimple and low cost fiber optic rotary coupler design.

It is a further object of this invention to provide a simple, low costoptical rotary coupler configuration which is adaptable to a largenumber of signal channels.

A further object is to provide a fiber optic rotary coupler wherein datais transmitted by light signals radiating transversely from or into anoptical fiber loop.

Yet a further object is to provide rotary coupler apparatus which iswell suited to both optical and electromechanical channels.

Additional objects of the invention may be ascertained from a study ofthe disclosure, drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view of multiple channel fiberoptic rotary coupler apparatus in accordance with the applicant'sinvention;

FIG. 2 is a cross sectional view of the fiber optic rotary couplerapparatus of FIG. 1 taken along lines 2--2, the elements being arrangedto transmit signals in one direction across a rotating/stationaryinterface;

FIG. 3 is a cross sectional view of the fiber optic rotary couplerapparatus of FIG. 1 taken along lines 3--3;

FIG. 4 is an illustration of a bent optical fiber demonstrating theprocess by which light is transversely radiated from the bent fiber; and

FIG. 5 is a cross sectional view similar to the cross sectional view ofFIG. 2, but wherein the elements are arranged to transmit signals in theopposite direction across the rotating/stationary interface.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, reference numeral 10 generally identifies multiple channelrotary coupler apparatus in accordance with the applicant's invention.Apparatus 10 comprises a first member 11 including a flange 12 tofacilitate attachment to a first body which may comprise a portion ofequipment in which it is necessary to transmit signals across arotating/stationary interface. As shown in FIGS. 1-3, member 11 isconfigured as a barrel having a circular cross section.

Member 11 is carried in a member 13 by means of a pair of bearings 14and 15, and is rotatable relative thereto about an axis of rotation 16.Member 13 incudes a flange 17 to facilitate attachment to a second bodywhich also comprises a portion of equipment in which transmission ofsignals across a rotating/stationary interface is required. As shown inFIGS. 1-3, member 13 is configured as a sleeve extending over barrel 11along axis 16.

For illustrative purposes, coupler apparatus 10 is shown with twooptical channels 18 and 20 and an electromechanical channel 22. Bothoptical channels are identical. Only channel 18 will be described indetail.

Channel 18 includes a first light transmitting fiber 24 which is woundin at least one complete circular loop 25 around the periphery of barrel11. Both ends of fiber 24 are routed through holes 26 and the hollowinterior of barrel 11 to a light source 27 in a fixed position relativeto the barrel. Light source 27 may comprise a light emitting diode whichradiates a light signal in response to electrical signals suppliedthereto on leads 28. As will be explained with reference to FIG. 4,light source 27 is oriented to radiate a light signal into at least oneend of fiber 24 from a direction within the cone of acceptance of theend of the fiber. Loop 25 is centered on axis 16 and generally lies in aplane perpendicular to the axis. Loop 25 radiates a light signal in acontinuous ring transverse to the axis of fiber 24 in the plane of theloop.

FIG. 4 shows an enlarged view of a portion of a light transmitting fiber30 having a light emitting diode 31 positioned and oriented to radiate alight signal into an end of the fiber. Fiber 30 is a conventional lighttransmitting fiber comprising a core 32 surrounded by cladding 33, thecore and cladding having different indices of refraction. Light radiatedinto an end of fiber 30 from a direction within a cone of acceptancerepresented by lines 34 is longitudinally transmitted through the fiberby total internal reflection. More specifically, light entering the endof fiber 30 from within the cone of acceptance is incident on thecore/cladding interface at an angle no greater than a critical angle α.Under such conditions, light continues to propogate along the fiber asillustrated by the rays within the straight portion of the fiber.

However, if fiber 30 is bent into a radius R as illustrated, the angleof incidence of a ray near the critical angle in the straight portion offiber 30 may exceed the critial angle at the outer core/claddinginterface in the bent portion of the fiber. As illustrated in FIG. 4,the critical angle has been exceeded by rays 35, 36 and 37 at 38, 39 and40 respectively. Under such circumstances, light radiates from fiber 30transverse to the longitudinal axis of the fiber. Reference may be madeto U.S. Pat. Nos. 3,936,631 and 3,982,123 issued respectively to W. M.Muska and J. E. Goell et al. on Feb. 3 and Sept. 21, 1976 for additionalexplanation of the foregoing phenomena in connection with fiber opticpower taps.

As shown in FIG. 2, barrel 11 is sized so that loop 25 has a radius R.Accordingly, loop 25 radiates a light signal in a continuous ring in theplane of the loop. The light signal is detected by light detector meansshown in FIGS. 1 and 2 as comprising light transmitting fibers 42 and42a. Each of these fibers has one end positioned by sleeve 13 so as tolie in the plane of the loop, the fiber end being oriented toward anouter surface of the loop at an acute angle which will provide forreception of transversely radiated light signals. A suitable orientationangle, as shown in FIG. 4, is an angle at which rays 35, 36 and 37 exitfrom fiber 30. Light signals entering opposite ends of fiber 24 areradiated from loop 25 in directions which have opposite components alongthe longitudinal axis of the fiber. Hence, detector fibers 42 and 42amay be advantageously used to achieve redundant signal transmission.

Fibers 42 and 42a are routed along the exterior of sleeve 13 to a lightdetector or photodetector 43 in a fixed position relative to the sleeve.Accordingly, light signals radiated from loop 25 are transmitted byfiber 42 to detector 43 where they are converted to electrical signalson leads 44.

Alternatively, fibers 42 and 42a could be omitted and one or moredetectors 43 positioned to directly receive light signals radiated byloop 25. In addition, either embodiment might advantageously employ someform of baffling between adjacent channels to prevent cross coupling oflight signals. One suitable baffle design comprises an opaque annulardisk or washer mounted between adjacent channels in a plane parallelwith the planes of the fiber loops. The washer would extend radiallyfrom the exterior surface of drum 11 nearly to the interior surface ofsleeve 13. Accordingly, it would prevent light from one fiber loop fromreaching the light detector means in adjacent channels.

Electromechanical slip ring channel 22 is of conventional design.Briefly, it comprises a conductive ring 46 carried on barrel 11 in aplane parallel with and spaced from the planes of the fiber opticchannels. Conductive ring 46 has an outer surface configured with anannular V-shaped groove therein in which a brush or slider element 47rides. Slider element 47 is mounted in a block 48 which is carried onsleeve 13. The electrical signals on ring 46 and slider 47 are carriedtherefrom by means of leads 49 and 50 respectively. Because of thegeometrical similarities between the fiber optic and electromechanicalchannels, it is apparent that both types of channels may be readilyincorporated into a single device in quantities required for anyparticular application.

The disclosed fiber optic loop configuration is inherently bidirectionalin that appropriately directed light signals will enter loop 25transverse to the longitudinal axis of the optical fiber. With referenceto FIG. 4, light signals will follow rays 35, 36 and 37 in a directionopposite to the indicated direction. FIG. 5 illustrates a fiber opticrotary coupler channel utilizing this characteristic.

Several of the elements forming the channel shown in FIG. 5 areidentical to elements shown in FIG. 2. More specifically, a barrel 11'is rotatably carried in a sleeve 13'. An optical fiber is wound onbarrel 11' in at least one complete circular loop 25'. A pair of lightsources 52 and 52a are mounted within sleeve 13' in the plane of loop25'. The sources are oriented to project light signals toward loop 25'in such a direction that the signals will enter the fiber. The ends ofthe fiber (not shown) are positioned to radiate the signals to one ormore light detectors. Accordingly, light signals may be transmittedacross a stationary/rotating interface from sleeve 13' to barrel 11'.

A preferred embodiment and several variations of fiber optic rotarycoupler apparatus in accordance with the applicant's invention have beenshown and described for illustrative purposes. Other embodiments whichdo not depart from the teaching herein will be apparent to those skilledin the art. The applicant does not intend that coverage be limited tothe disclosed embodiment and variations, but only by the terms of theappended claims.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:
 1. Fiber optic rotary couplerapparatus for transmitting light signals between first and secondbodies, one of which is rotatable relative to the other about an axis ofrotation, comprising:a first light transmitting fiber of a type throughwhich light is longitudinally transmitted by total internal reflectionif said fiber is maintained at a radius no smaller than a predeterminedcritical radius, and from which light escapes transverse to the lengthof said fiber if said fiber is bent into a radius within a predeterminedrange of radii smaller than the critical radius; a first member adaptedto be fixed to the first body, and adapted to carry said lighttransmitting fiber so that it is maintained in at least one completecircular loop having a radius within the predetermined range, the loopbeing centered on the axis of rotation and generally lying in a firstplane perpendicular thereto; a first light source fixed relative to thefirst body and oriented to project a light signal into an end of saidfirst light transmitting fiber; first light detector means; and a secondmember adapted to be fixed to the second body, and adapted to carry atleast part of said first light detector means so that it is positionedto receive light signals which escape from said first light transmittingfiber.
 2. The fiber optic coupler apparatus of claim 1 wherein:saidfirst member comprises a barrel extending along the axis of rotation andhaving a radius within the predetermined range of radii; said firstlight transmitting fiber is wound around said barrel to form a completecircular loop; and said second member comprises a sleeve extending oversaid barrel along the axis of rotation.
 3. The fiber optic couplerapparatus of claim 2 wherein said first light transmitting fiber isconfigured so that both ends thereof are positioned to receive lightsignals from said first light source.
 4. The fiber optic couplerapparatus of claim 2 further including:a second light transmitting fibersimilar to said first light transmitting fiber, said second lighttransmitting fiber being wound around said barrel so as to form acomplete circular loop centered on the axis of rotation and generallylying in a second plane parallel with and spaced from the first plane; asecond light source fixed relative to said first body and oriented toproject a light signal into an end of said second light transmittingfiber; and second light detector means at least partially carried bysaid sleeve so that it is positioned to receive light signals whichescape from said second light transmitting fiber.
 5. The fiber opticcoupler apparatus of claim 4 wherein each of said first and second lightdetector means includes a further light transmitting fiber interposedbetween one of said first and second light transmitting fibers and alight detector associated therewith, said further light transmittingfiber having a first end carried by said sleeve and oriented toward theloop in the associated light transmitting fiber at an acute anglerelative to the length of the fiber, and a second end positioned totransmit light signals to the associated light detector.
 6. The fiberoptic coupler apparatus of claim 5 wherein said first and second lighttransmitting fibers are each configured so that both ends thereof arepositioned to receive light signals from the light source associatedtherewith.
 7. The fiber optic coupler apparatus of claim 6 furtherincluding an electromechanical slip ring channel comprising:a contactring carried on said barrel in a third plane parallel with and spacedfrom the first and second planes; a slider element carried within saidsleeve and positioned to engage said contact ring; and means forconducting electrical signals to said contact ring and said sliderelement.
 8. Multiple channel fiber optic rotary coupler apparatus forsimultaneously transmitting a plurality of light signals between tworelatively rotatable bodies, comprising:a barrel of a predeterminedradius adapted to be connected to one of said bodies; a sleeve adaptedto be connected to the other of said bodies; bearing means for carryingsaid barrel within said sleeve so as to permit relative rotation aboutan axis; a plurality of light transmitting fibers wound on said barrelso that each forms at least one complete circular loop centered on theaxis and generally lying in a separate plane perpendicular to the axis,each of said light transmitting fibers being operable by total internalreflection to longitudinally transmit a light signal introduced into anend thereof when said fiber is maintained at a radius larger than thepredetermined radius, and to transversely radiate a portion of the lightsignal when said fiber is bent into the predetermined radius; aplurality of light sources, each positioned to project a light signalinto an end of a separate one of said plurality of light transmittingfibers; and a plurality of light detector means at least partiallycarried by said sleeve, each light detector means being positioned toreceive light signals transversely radiating from a separate one of saidplurality of light transmitting fibers.
 9. The fiber optic couplerapparatus of claim 8 wherein each of said plurality of light detectormeans includes a further light transmitting fiber interposed between theassociated one of said plurality of light transmitting fibers and alight detector associated therewith, said further light transmittingfiber having a first end carried by said barrel and oriented toward theloop in the associated light transmitting fiber at an acute anglerelative to the length of the fiber, and a second end positioned totransmit light signals to the associated light detector.
 10. The fiberoptic coupler apparatus of claim 9 wherein each of said plurality oflight transmitting fibers is configured so that both ends thereof arepositioned to receive light signals from a separate one of saidplurality of light sources.
 11. The fiber optic coupler apparatus ofclaim 10 further including means for converting at least one of thelight signals into a corresponding electrical signal.
 12. Fiber opticrotary coupler apparatus for transmitting light signals between firstand second bodies, one of which is rotatable relative to the other aboutan axis, comprising:a light transmitting fiber of a type through whichlight is longitudinally transmitted by total internal reflection if saidfiber is maintained at a radius no smaller than a predetermined criticalradius, said light transmitting fiber being capable of receiving lightdirected transverse to an outer surface of said fiber at a locationwhere said fiber is bent into a radius within a predetermined range ofradii smaller than the critical radius; a first member adapted to befixed to the first body, and adapted to carry said light transmittingfiber so that it is maintained in at least one complete circular loophaving a radius within the predetermined range, the loop being centeredon the axis of rotation and generally lying in a first planeperpendicular thereto; a light detector fixed relative to the first bodyand oriented to receive a light signal from an end of said lighttransmitting fiber; light source means; and a second member adapted tobe fixed to the second body, and adapted to carry at least part of saidlight source means so that it is positioned to radiate light signalswhich will be received by said light transmitting fiber.
 13. The fiberoptic coupler apparatus of claim 12 wherein:said first member comprisesa barrel extending along the axis of rotation and having a radius withinthe predetermined range of radii; said light transmitting fiber is woundaround said barrel to form a complete circular loop; and said secondmember comprises a sleeve extending over said barrel along the axis ofrotation.
 14. The fiber optic coupler apparatus of claim 13 wherein:saidlight transmitting fiber is configured so that both ends thereof arepositioned to transmit light signals to said light detector; and saidlight source means includes two light sources positioned to radiatelight signals in directions which have opposite components along thelongitudinal axis of said light transmitting fiber.